1. Field of the Invention
The present invention relates to the mounting of a suspension member for a turbine engine such as a turbojet engine. It relates in particular to the mounting of a suspension member comprising a means aimed at preventing the suspension pin from rotating so as to avoid the problems that result from pin vibration and wear.
2. Description of the Related Art
A propulsion engine, such as a turbojet engine, may be mounted at various points on the airplane by being attached to a strut belonging to the structure of this airplane. It may be suspended under the wings, fixed to the fuselage or mounted in the empennage using attachment means. The purpose of these attachment means is to transmit mechanical load between the engine and the structure of the turbojet engine. The loads that have to be taken into consideration are directed in the three main directions. These are, in particular, the weight of the engine, its thrust, and lateral aerodynamic loadings. The loads that need to be transmitted also include reacting the torque about the axis of the engine. These means have also to absorb the deformations experienced by the engine during the various phases of flight on account in particular of dimensional variations due to thermal expansion or contraction.
One method of suspension, for example in the case of a turbofan engine, is to attach the engine to a strut belonging to the structure of the wing of the airplane using a forward suspension or hard point and a rear suspension or hard point. The forward suspension is fixed in particular to the intermediate casing downstream of the fan casing and the rear suspension is fixed to the jet pipe.
In a known configuration, the forward suspension is designed to transmit vertical and tangential mechanical load between the engine and the airplane. The rear suspension is designed to transmit mechanical load in these same directions and to react engine torque about the axis of the turbojet engine and to react thrust. The latter is transmitted via two thrust reaction rods attached, at the front, to the base of the intermediate casing on each side of the longitudinal axis and, at the rear, to the engine rear suspension means.
In general, a suspension means comprises a beam, possibly a double beam, fixed to the strut by bolts and connected to the engine casing by link rods. The link rods swivel at their ends in yokes or brackets, depending on how they are mounted, secured respectively to the casing and to the beam. In order for the load transmitted through the link rods to be purely axial, a ball swivel is provided on the through-pins, at each end thereof. This method of mounting in particular makes it possible to absorb the radial and axial expansions of the engine.
As depicted in FIG. 1, a link rod 30 is fixed to the lugs 20 and 21 of a casing yoke via a stepped pin 22, fixed by two bushings 40 and 50 to the two lugs, passing through the top end of the link rod. The link rod 30 has a bore into which there is set a cage 35 with a spherical interior surface. The latter acts as a guide for a ring 70 with a spherical exterior surface, fixed to the pin, thus forming a ball joint. There is clearance between the bushings and the ball 70. The ball can move axially along the pin. Said pin is held in place by a nut and a washer with clearance between the washer and the lug of the yoke.
Thanks to this ball-joint setup, the top of the link rod can pivot not only about the pin but also about any axis perpendicular thereto within the limits of the end stops defined by the surroundings. The movement is limited particularly according to the space, left on each side, between the top of the link rod and the lugs of the yoke. One exemplary embodiment of a link rod suspension device is given in patent application FR 0 357 504.
Over the course of the life of the engine, the connecting pin is made to undergo microscopic movements due to vibrational loadings, and in particular to influences directed parallel to the pin, particularly on account of the fact that the link rods are slightly inclined with respect to the casing. Over time, repeated influences of this type cause frictional wear on the pin and on the bushings. In addition, the change in diameter of the casing, as a result of expansion, associated with a distributed load over the link rods may cause the pin to rotate about its mount.
The applicant company has set itself the objective of mounting a suspension member on turbine engine casing yokes that is able to avoid the wear problems due to friction at the lugs, at the bushings and at the suspension pins by preventing said suspension pin from rotating.